Background: We hypothesized that in acute lung injury (ALI), the volume of pulmonary tissue with aqueous density, as determined by spiral computed tomography (CT), is associated with extravascular lung water content. Our aim was to compare tissue volume index, as assessed by CT, before and after oleic acid-induced ALI, with extravascular lung water indexes (EVLWI), determined with single transpulmonary thermodilution (EVLWISTD), thermal-dye dilution (EVLWITDD), and postmortem gravimetry (EVLWIG).
Methods: Seven instrumented sheep received an intravenous infusion of oleic acid 0.08 ml/kg (OA group) and four animals had vehicle only (Control group). The day before, and immediately after the experiment, sheep were anesthetized to undergo quantitative CT examinations during a short breath hold. Hemodynamics, oxygenation, EVLWISTD, and EVLWTDD were registered. Linear regression analysis was used to assess the relationships between EVLWISTD, EVLWTDD, EVLWIG, and lung tissue volume index (TVICT) determined with CT.
Results: In the OA group, total lung volume increased compared with Controls. Poorly and non-aerated lung volumes increased a 3.6- and 4.9-fold, respectively, and TVICT almost doubled. EVLWISTD, EVLWITDD, and TVICT were associated significantly with EVLWIG (r=0.85, 0.90, and 0.88, respectively; P<0.001). TVICT deviated from the reference EVLWIG values to the greatest extent with a mean bias ± 2SD of 4.0 ± 6.0 ml/kg.
Conclusions: In ovine oleic acid-induced ALI, lung tissue volume, as assessed by quantitative CT, is in close agreement with EVLWI, as determined by indicator dilution methods and postmortem gravimetry, but overestimates lung fluid content.